Does not expire, it always stays fresh. As a water purifier add 3-6 drops per liter of water. No need to refrigerate, but keep out of direct sunlight. Natural water purifier, solution consists of 85% distilled water, 10% Potassium Iodide and 5% Iodine. Iodine is necessary for the thyroid gland's proper performance of its work. We usually get iodine from our diet, however the soil is depleted of essential nutrients and iodine is one of those minerals. Take an iodine supplement for thyroid health and support immune health. In Japan the average consumption of iodine is 10-14 mg daily.